Thursday, May 25, 2017

Sun Compass - How to do a daytime polar alignment


One of the challenges of setting-up telescope equipment at a public star party is you need visible stars in order to polar align your telescope mount. But, it's just at that time that the visitors are curious and want to ask questions, God bless 'em.

So, for some time now, I've used the azimuth of the Sun (from the SkySafari Info screen below) to set-up my tripod before dark, or at any time of day, say for a solar observing event, such as an eclipse.

When the sun angle is 270° (Sun directly West), it's a piece of cake - arrange the two southward facing legs so that the shadows overlap. (See Morning Example, below.)

But, what do you do between Fall and Spring, when the Sun doesn't reach as far North as 270°? And, what if you want to set-up any other time of day? Maybe you waited too late and missed the 270° mark?

So, using the azimuth of the Sun reading, found in SkySafari, I used this contraption to line up it's shadow with the SS reading of 276° and 4 min.

Now, for this to work, one has to reverse the cardinal direction readings, since you want to point to where the Sun's shadow is coming from. Hence, 270° is on the right (east, as I'm looking at it). North is up.



















Also note this is not affected by the Equation of Time since that is figured in with the SS azimuth reading.

So, all one has to do is set this sun compass under or near your tripod, orient the shadow to agree with SkySafari's listed azimuth of the Sun (or, whatever source you customarily use) and aim your third tripod leg to where North is indicated.

Now, we just need a Star Party.

Morning Example - taken when the Sun was at an azimuth of 75°.





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